The clash between reason and Portuguese experience.Hooykaas' starting point is the intellectual challenge which, from the early 15th century onward, was posed by the discoveries of the Portuguese mariners... There follows an array of fascinating accounts of, and quotations from, works by contemporary authors who were compelled to face as facts numerous phenomena the ancients had been quite sure could not possibly be observed because they were bound not to exist. Examples are Aristotle's denial that the tropics could be inhabited; Ptolemy's mathematically derived conviction that all dry land is confined to part of the Northern Hemisphere, and so on. ...In Hooykaas' view we are witnessing here a birth of 'natural history' in the domain of the hard and given fact... The narrow world of sense-data to which the ancient natural philosophers had confined their all-too-rational speculations was now being blown to pieces. And this was not being done by fellow natural philosophers, but rather at the urging of scarcely literate sailors!